Answer
In 2012, Petra Kvitová defeated world No. 5, Samantha Stosur, in the Wimbledon Championships. This was a major upset, as Stosur was considered one of the favorites to win the tournament. Kvitová, on the other hand, was not ranked as highly and was not expected to do well. However, she played a very strong match and was able to defeat Stosur in straight sets.